Low-Temperature Embedding in Acrylic Resins

It has been demonstrated that enzymes (5 ,6 ) can maintain their structure and their activity at very low temperature in concentrated organic solvent. Therefore, in order to minimize molecular thermal vibration, which can have adverse effects on specimens weakly fixed with paraformaldehyde, one can dehydrate samples partially or totally at low temperature. Carlemalm et al., 1982 (3 ) introduced the PLT technique (progressive lowering of temperature) that combines increasing organic solvent concentration with decreasing temperature, after which infiltration and polymerization are carried out. The results obtained with Lowicryls clearly show the advantages of this approach to obtain good structural preservation of cellular contents and ultrastructure. Furthermore, the PLT method employs low temperature to reduce protein denaturation and to maintain a degree of hydration, which may be important in preserving protein structural conformation. Specimens suffer most during dehydration by organic solvents, mainly ethanol, whereas final infiltration by resin monomers and polymerization seems to be less critical.